Multiband tuner



1953 v. P. FRIBERG 2,648,824

MULTIBAND TUNER Filed Jan. 16, 1951 2 Sheets-Sheet l j ff' 1/ .12;- 32 xi INVENTOR. I VINCENT RFRfiBERG.

1 BY W44 Maw l A TTO/FNEYS.

V. P. FRIBERG MULTIBAND TUNER Aug. 11, 1953 2 Sheets-Sheet 2 Filed Jan. 16, 1951 INVENTOR. VINCENT P. FRIBEEG.

A T TORNEK5.

Patented Aug. 11, 1953 MULTIBAND TUNER Vincent 1. Friberg, Lyndhurst, N. J assignor to Automatic Manufacturing Corporation, Newark, N. J., a corporation of New Jersey Application January 16, 1951, Serial No. 206,245

19 Claims. 1

This invention relates to a multi-band tuner and more particularly to a device for continuously varying the resonant frequency of a tuned circuit over two different frequency bands which may be immediately tuned adjacent or separated.

Tuned circuits comprising an inductance and a condenser or comprising an inductance which resonates with its distributed capacity are well known. It is also known to tune such circuits by varying the condenser or by varying the reactance of the inductance with a movable magnetic core. However, in the past it has been difficult to tune such circuits over a wide frequency band and to tune such circuits over two different frequency bands without the use of complicated mechanical arrangements, such as separate band switches, rotary turrets or manually replaceable components.

It is an object of my invention to provide a I multiband tuner which is simple and which is only a single tuning control for operation over a plurality of frequency bands.

Other objects and advantages of my invention will be apparent from the detailed description of the invention given hereinafter by way of example only and setting forth the manner in which I now prefer to practice the invention.

In accordance with my invention, a core, one portion of which is magnetic but of low conductivity and another portion of which is highly conductive, is mounted adjacent a coil or coils having the shape of a portion of a toroid. As the core is moved relative to the coil or coils or vice versa, the reactance of the coil or coils is varied, and a switch associated with the core adjusting mechanism changes the portion of the coil or the particular coil which is operative in the tuned circuit.

In accordance with th preferredembodiment of my invention, the core is toroidal in shape and the entire core is formed from a magnetic composition, such as powered iron embedded in thermo-plastic material. A portion of the core is coated with a conductive layer, such as silver. The core passes through a pair of coils which have the shape of a portion of a toroid, and both of which are operative when the magnetic, low

conductivity portion is therein and when the magnetic, low conductivity portion is within one coil and the conductive portion is within the other coil but only one of which is operative when the conductive portion is within the other coil.

My invention may be better understood by referring to the following detailed description of the invention and to the accompanying drawings, in which:

Fig. 1 is a side elevation view of one embodiment of my invention;

Fig. 2 is an end elevation view partly in section of the embodiment shown in Fig. 1 and taken along the line 22 indicated in Fig. 1;

Fig. 3 is an end elevation view partly in section of the embodiment shown in Fig. 1 and taken along the line 3-3 indicated in Fig. 1;

Fig. 4 is a fragmentary sectional view of a coil form support employed in my invention taken along th line 44 indicated in Fig. 3;

Fig. 5 is a fragmentary sectional view of a magnetic core employed in my invention taken along the line 55 indicated in Fig. 3;

Fig. 6 is an electrical circuit diagram of the embodiment of my invention shown in Figs. l-5;

Fig. '7 is an end elevation view partly in section of a modified form of my invention;

Fig. 8 is a fragmentary side elevation view of the modified embodiment shown in Fig. 7; and

Fig. 9 is an electrical circuit diagram of the embodiment of my invention shown in Figs. '7 and 8.

Referring to Figs. 1-5, the preferred embodiment of my invention comprises a shaft In which is manually rotatable, such as by a knob I I, and which is rotatably mounted in a pair of brackets I2 and I3. The brackets I2 and I3 may be mounted on a base I4 to which the brackets are secured by any suitable fastening means, such as screws I5.

Longitudinal displacement of the shaft I0 is prevented by collars I6 and I! which are secured to the shaft I0 and which are rotatable therewith. The collars I6 and I1 bear against the brackets I2 and I3 and have reduced portions thereon which carry arms IB and Q9. The arms I8 and I9 preferably are formed from insulating material and may, for example, be pressed on the reduced portions of the collars It and I1 so as to be rotatable with the collars I6 and I1 and the shaft I8. At their outer extremities, the arms I8 and I9 have apertures into which a shaft 20 may be inserted. The shaft 26 may be held in the apertures in the arms I8 and I9 by means of a bifurcated washer 2| which engages notches in the shaft 26 and by a shoulder 22 at one end of the shaft. Thus, when the shaft II) is rotated, the shaft 20 revolves about the axis of the shaft It.

A hollow coil form 23 having the shape of a formed from two members 28 and 29 of insulating, material which clamp the members 23 and 21" together and the members 23 and 233 may be: pressed together by any suitable fastening means, 'Ihemembers 28; and

such as rivets 3c and 3!. 29 may have grooves therein which .are semi-circular in cross section and which snugly receive the members 23 and 21 of the coil form-:23.-

A pair of coils 32 and 33 are mountedon the coil form 23 and also have the shape of a portion of a toroid. The coils 32 and 33 may be considered as two separate'coils or may be considered as a single coilcomprising two spaced portions. As used in this specification andthe appended claims, the word coil is intended to include not only a continuous untapped winding of conductive material but also a plurality of windings of the same or'differ'ent conductive material or arrangement, the windings being connected electrically in series.

As shown, the coil 32 has a fewer number of turns than the coil 33 and the strip material used for the'turns f coil'32 has a greater cross section than the strip material used-for the turns of the coil'3'3: The coils32 and 33 illustrated in the drawings havebeen constructed so as to provide a tuner which will tune over a pair of widely separated frequency bands. However, the coils 32 and 33' may have other arrangements orconstructions' wellknown to thoseskilled in the art for, the purpose of tuningover different frequency bands which may be adjacent to each other'or widely separated.

A thirdcoillS lmay be'woun'd about both of the coils 32Land33f0r the purpose" of loading'the coils 32 and 33'or'for the purpose of coupling other: circuits to the coils 32'and33. Preferably, the coil '36 is separated from the coils 32 and 33' by a layer of insulating material, such as insulatingtape, which maybe wound about the coils 32 and 33.

A magneticcore 35 having the same centerof curvature asthe coil form 23 and the coils 32, 33 and 34 is mounted coaxially with the shaft 59 and with a portion thereof inside the coil form 23. The core 36 is similar to the core described in theco-pending application Serial No. 101,713 of Lyman G; Ketcham,.filed June 28, 1949, and is preferably acomplete toroid, as shown, but may be" discontinuous and have the shape of a portion of a toroid. The. core 36 has a first portion 3'! of "magnetic material of relatively low conductivity which in. the drawings is' shown within the coil form 235 Theremaining portion 38 of the core 36 has'a relatively high conductivity for purposes which will be hereinafter described. Preferably, the core dfi isconstructed'by first forming a toroidal core of powdered magnetic material in a well known manner; the particles'ofmagnetic material being insulated from each other. The core 35 may, for example, be formed from a mixture of powdered iron'in'a resin binder. After. the core 36 is formed, the portion 38 is coated with a layer 3'9of a material having a high conductivity, such as silver, copper, or aluminum. In the embodimentshown, the. layer 39 ofmaterial of high con- 4 ductivity covers substantially one half of the core 33 in the circumferential direction lying in the plane of rotation of the core 36.

Preferably, the core 35 slides within the coil form 23 and may be rotated by an arm 4i] which engages the shaft 20 and which may be cemented to the core 33 in a notch therein. However, if desired, the, core 3% may be of such a size that a small space is left between the core 35 and the interior wall of'the coil form 23 and the core 36 may be entirely supported. from the shaft l0 so as to avoid frictional contact between the core 3.6fiandfthe coil form 23.

When theportiona'il of low conductivity and high permeability is within the coils 32 and 33, thesecoils-have the highest value of inductance. When, however, the high conductivity portion of the core-35is within the coils 32 and 33, these coils have the lowest value of inductance. According- 1y, as the core 3E3 is rotated, the inductance of the coils changescontinuously from a high value to a low value and if-the coils are merely connected in series; theywill act as a timed circuit which may be tuned over a single wide frequency band. However, in accordance with my invention, provisions aremade for rendering one of the coils inoperative during the passage of a predetermined portion ofthe c-ore'throughthe other of the coils.

Referring particularly to Figs. 1 and2, it will be seen that one end ofthe coil 32 is connected to one' terminal of a padding condenser ll, the other-end ofthe condenser M being connected to a grounding lug 42; The other end of the coil 32iis' connected to a stationary contact 43 mounted on'the'insulating block 23. One end of coil 33 is also. connected-to the stationary contactl3-and the other end of coil 33 is connected-to a second stationary contact 43 which is also connected to a grounding lug 33. The coils 32- and 33 are, therefore, connected in series with each-other and the two series connected coils are connectedin parallel withthe padding condenser ll A' movable contactor d3 of conductive material, such' as copper, brass, etc., is mounted on an insulating disc 41 which in turn is mounted on the shaft iii and has an arm portion 38 which engages the shaft 2!}. The contactor 36' may be fastened to the insulating disc, by mean of rivets i9 and as the shaft Wis rotated, theinsulating disc 41 andthe contactor l6 are rotated therewith.

The contactor 66 has two arcuate portions 50 and 5! which extend, different distances radially from the axis of the shaft iii. The stationary contacts 43' and 45 also have different lengths so that the stationary contact M maintains contact with the contactor 46 at all times; However, the stationary ccntact l3 engages the contactor 36 only when the arcuate portion 593 is rotated so as to be directly. underneath the contact 33. The arcuate portion 501s so disposed with respect to theconduotive layer 39"0n the portion 330i the core..36"thatlit engages contact 33 as the portion 38 enters the coil 32: and remains in engagement with the contact 43 during movement of the portion 38'through the coil 32. It will be seen, therefore,,that withthe arrangement shown in Figs. land 2., the two coils 32 and33 during approximatelydegrees of rotation of the shaft l0 act as a single coil, a portion of which has a continuously decreasing inductance during the rotationof the shaft it As soon as the portion 58 engageszthe stationary contact 43, the coil 33 is rendered inoperative by virtue of the connection between the stationary contact 13, the contactor 46 and. the-stationary contact. Mwhich short.-

circuits the coil 33. During the remaining rotation of the shaft H) in the clockwise direction as viewed in Fig. 2, only the coil 32 is effective and its inductance is continuously decreased from the value of inductance at the time the portion 59 engages the contact 43.

The electrical operation of the invention may be better understood by referring to Fig. 6 which shows an electrical diagram of the embodiment shown in Figs. 1-5. As shown in Fig. 6, the coils 32 and 33 both have a variable inductance and the coil 33 is short-circuited during one portion of the rotation of the shaft l0. During one portion of the rotation of the shaft H], the circuit resonates at a frequency determined by the sum of the inductance of the coils 32 and 33, the stray capacities of the circuit, and the condenser 4|. However, as soon as the contacts 43 and 44 are connected together by the contactor 46, the frequency of resonance is determined by the inductance of the coil 32 alone, the stray capacities of the circuit, and the condenser 4|. Accordingly, during one portion of the rotation of the shaft ID, the circuit tunes over a wide band of relatively low frequencies and after the coil 33 is short-circuited, the circuit tunes over a Wide band of relatively high frequencies.

It will be noted in connection with the description given above, that the band of relatively low frequencies is not independent of the coil 32. Therefore, as the number of turns and the spacing of the turns of the coil 32 are varied to adjust the band of frequencies covered by the coil 32, the band of frequencies covered by the coils 32 and 33 connected in series will also be varied. If it is desired to make the tuning of the circuit over the band of relatively low frequencies independent of the tuning of the coil 32, the embodiment shown in Figs. 1-5 may be modified, as shown in Figs. 7 and 8.

The modified embodiment shown in Figs. 7 and 8 differs from the embodiment shown in Figs. 1-5, substantially only in the shape of the contactor employed and by the addition of a third stationary contact which engages the contactor. The contactor 52 shown in Figs. 7 and 8 has three arcuate portions 53, 54 and 55, the portions 53 and 55 extending substantially the same distance radially from the axis of the shaft l and the portion 54 extending a shorter distance radially from the axis of the shaft ID. A stationary contact G is mounted on an insulating block 51 and is engageable with the portion 55. The insulating block 51 may be held on the base H by any suitable fastening means, such as screws 58. One end of the coil 32 is connected to the stationary contact 56 and the other end of the coil 32 is connected to a stationary contact 59 which is longer than the contact 56. One end of the coil 33 is also connected to the contact 59 and the other end of the coil 33 is connected to a stationary contact 60 which is engageable with the portion 53 of the contactor 52 but which cannot engage the portion 54 of the contactor 52.

During approximately the first 90 degrees of rotation of the shaft ID from the position shown in Fig. 7, the coil 32 is rendered inoperative by virtue of the connection between the contact 56 and the portion 55 of the contactor 52 and between the contact 59 and the portion 54.v However, during this portion of rotation of the shaft Hi, the coil 33 is operative and the resonant frequency of the circuit is determined by the inductance of the coil 33, the stray capacities of the circuit, and the padding condenser 4|. During 6 the remaining portion of the rotation of the shaft ID, the coil 33 is rendered inoperative'by virtue of the connection between the contacts 59 and so and the portion 53 of the contactor 52, and the coil 32 in conjunction with the stray capacities of the circuit and the condenser 4| determines the resonant frequency of the circuit. The coil 32 is operative during the remaining portion of rotation of the shaft l0 because the contact 56 is out of engagement with the contactor 52.

Referring to Fig. 9, which shows an electrical diagram of the embodiment illustrated in Figs. 7 and 8, it will be seen that during one portion of the rotation of the shaft II], the resonant frequency of the circuit may be continuously varied by the inductance coil 33 and during the remaining portion of the rotation of the shaft II], the resonant frequency of the circuit may be continuously varied by the inductance coil 32. The arrangement in Figs. 7 and 8 accordingly provides a tuned circuit which is continuously variable over two wide frequency bands and each coil forming part of the tuned circuit may be adjusted substantially without affecting the band of frequencies over which the circuit may be tuned when the other coil is operative.

Having thus described my invention with particular reference to the preferred form thereof and having shown and described certain modifications, it will be obvious to those skilled in the art to which the invention pertains, after understanding my invention, that various changes and other modifications may be made therein without departing from the spirit and scope of my invention, as defined by the claims appended hereto. The number and arrangement of the stationary contacts and the shaping and arrangement of the stationary contactor may, for example, be modified so as to provide other connections of the coils which determine the frequency bands over which the circuit may be tuned. Furthermore, one or more of the tuners shown in the various figures may have their shafts mechanically connected together and may be used to tune concurrently one or more stages of an amplifier or receiver.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A multi-band tuner comprising a coil element; a core element mounted adjacent said coil element,said core element having a first portion of magnetic material of low conductivity and a second portion of relatively high conductivity and said core element and said coil element being movable with respect to each other; means for moving one of said elements with respect to the other of said elements; and switch means connected to said coil element and adapted to switch a portion of said coil element out of circuit with another portion of said coil element, said switch means being connected with said moving means and being operated thereby in the position thereof in which a predetermined one of said portions of said core element is adjacent said other portion of said coil element.

2. A multi-band tuner comprising a coil, a core of magnetic material of relatively low conductivity mounted with a portion thereof within said coil, said core being movable within said coil and having a layer of material of relatively high conductivity covering a predetermined portion of the length of said core; means for moving said core with respect to said coil; and switch means connected to and adapted to short-circuit a portion of said coil, said switch means being operated by said moving means during movement 7 of said? high; conductivity; layer through, the re:- mainder of saidcoil;

3;. A multieband v tuner; comprising; a; pair of spaced; coils; a core of magnetic. material of: rel.- atively' low conductivityrmounted 5 With. a portion thereof within saidzcoils; said core beingmovable within. said Icoils: and having. a layer; of; material of relatively high conductivity-on. apredetermined? portion of thelength-oisaidzcore; means for movingsaid-zcore with reSpect-to-said-coils; and .switch means;connected .to one ofisaidcoils and adapted-to short-circuit said; one coil; said switch: means" being. operated. by said moving means during movement; of; said high conductivity: layer through the other: of said coils.

4. .A multi-ban-d tuner comprisinga pair of coils mounted in spaced; positions with respect to each other, said coils-being'connectediinseries with eachother; acore ofmagnetic-,material of low conductivity. mounted with a portion thereof Within said coils,.said corebeing movablewithin=said,- coils and having a; layer of material of higlrconductivity on a predeterminedportion of the length-oi said core; meansvfor moving; said core; apair-cr stationary contacts, one being connected to the adjacent connected ends of said coils and the other being connectedto the-opposite-end of one of saidcoils; andmeanscontrolledwith saidmovingmeans and adapted to interconnect said-stationary contacts whilesaid high conductivity layer is within the other of said coils,

5. A multi-bandtuner comprisingqa coilele: nienthaving the shape ofa-portionofa toroid;

a core elementmounted adjacentsaid coil and having the shape oiatleasta.portionof a toroid, saidicore elementhavingafirst portion of magneticrnaterial of low conductivity andv asecond portionof relatively high conductivity andsaid core element: and said coilelement being movable with respecttto each other; meansiior. moving one of said, elements with respecttoithe. other of said elements; and switch means connected to said coilelementand being. adapted. to switch a portion .of said. coilelement out of circuit with another portionofsaidcoil element, said switch means being; operated by said. moving means during relative movement. ofa predetermined one of said portions of saidcore element past saidother portion. of said coilelement.

6. A multi-band tuner comprisingapair. of coil elements, each having the shape. oiaportion of. atoroid; a core element mounted adjacent said coil elements and having the shape. of. at least a. portion. of a toroid, said. core element having a first portion of magnetic material of low. conductivity and a second portionof relatively. high conductivity and said core element and saidooil elements being movable with respect to each other;. means for moving one of said elements with respect to theother of'said' elements; and switch means connected to onev of said coil elements and adapted to switch. said one coil element out of circuit with. the other of said coil elements, said switch means being operated by saidmoving means during relative movement of a predetermined one of said portions ofsaid core element past the other of said coil'elements.

'7. A multi-band tuner comprising a coil having the shape of a portion of a toroid; a core mounted adjacent said coil and havingthe shape of atleast a portion of a toroid, said core having a..first portionof magnetic materialof low conductivity and a second portion of relatively high conductivity, and. said core and said: coilbeing movable with respect to each other; means-for rotatingtsaidcore and said coil relative toweach other; andswitch means connected to said. coil and adapted toswitch a portion of said coil;out of circuit with another portion ofsaidxcoil, said switch means being operated by said. rotating means; during-relativemovement of a predeterminedone of said portions of; said corepaistathe remainerofsaid coil..

8. A, multi-band, tuner. comprising a pair of coils having the shape ofa portion of atoroid; a core mounted adjacent said'coilsgand;having the-shape of at .leasta portion-of a, toroid, said core having a first portion ofmagnetiomaterial of low conductivity and'a second portion .ofyrelativelyhigh conductivity and saidcoreandsaid coils-being movable with respect to eachother; means. for rotatingsaid core-and saidcoils rel.- ativeto each other; and switch-means connected to'one of said coils andadapted to switch: one of saidcoils out of circuit withthe other of said coils, said switch means being operated by.. said rotating means during relativemovement of, a predetermined one of said portionsof said core past said other of said coils.

9. A multi-band tuner comprising acoil having the shape of a firstportionof atoroid; a core having a portion of magnetic material-of, rela: tively low. conductivity and havingthevshape of at least a: portion of. a toroid,.said core being mounted adjacent said .coil and said coreand said coil being movable With resp-ectwtoeachother, alayer of material of relatively highconductivity on a second portion-ofsaid core and covering-a predetermined length thereof in, a circumferen tial direction; meansfor rotating, said core and said .coil relative to, each other; and switch means connected to-said coil and adaptedto switcha portion of said coil out of circuit withithe remainder. of said coil, said switchmeans being operated by said rotating means during relative movement of a predeterminedone of. said portions of saidcore past saidremainder of. said coil.

10.. A multi-band tuner. comprising a. pair of coils having the shape of a portionof. atoroid; a core of magnetic material of relatively low conductivity. having the shape of ratflleast. a portion, of a. toroid and. mounted, with a portion thereof adjacent said coils; said. core. andsaid coilsbeingmovable with respectto each other andsaid corehaving. a layer. of.material of rel: ativelyv high conductivity thereon coveringarpredeterminedlength. thereof in a circumferential direction; means for rotatingsaid'core andsaid coils relative to each other; and switch means connected to one of. said. coils andv adapted, to switch one of, said coils outv of circuit. with the other of. said, coils, said switch means being operated by. said rotating. means during relative movement of a predetermined, portion of. said :ore past the other. of saidcoils.

11. A.multi-bandtuner comprising a coil having the shape of a portionof a toroid; a toroidal core. of magnetic material, ofrelativelyv low conductivity mountedwith a portion thereof; adja;- cent said. coil, saidcore having the same center of curvature. as. said coil and being movable with respect thereto anda layer of. materialof. r,ela. tively high conductivity on=saidcore covering a predetermined. length ofsaid core i in a circumferential direction; means for rotating-said core about its center of curvature;-andswitchmeans connected tosaida coil and. adapted tolswitch-a 9 portion of said coil out of circuit with the remainder of said coil, said switch means being operated by said rotating means during movement of said high conductivity layer past said remainder of said coil. 7

12. A multi-band tuner comprising a pair of coils having the shape of a portion of a toroid; a toroidal core of magnetic material of relatively low conductivity mounted with a portion thereof adjacent said coils, said core having the same center of curvature as said coils and being movable with respect thereto and a layer of material of relatively high conductivity on said core covering a predetermined length of said core in a circumferential direction; means for rotating said core about its center of curvature; and switch means connected to one of said coils and adapted to switch one of said coils out of circuit with the other of said coils, said switch means being operated by said rotating means during movement of said high conductivity layer past said other of said coils.

13. A multi-band tuner comprising a coil having the shape of a portion of a toroid; a toroidal core of magnetic material of relatively low conductivity mounted with a portion thereof within said coil, said core having the same center of curvature as said coil and being movable therein and a layer of material of relatively high conductivity on said core covering a predetermined length of said core in a circumferential direction; means for rotating said core about its center of curvature; and switch means connected to said coil and adapted to short-circuit a portion of said coil, said switch means being operated by said rotating means during movement of said high conductivity layer through the remainder of said coil.

14. A multi-band tuner comprising a pair of spaced coils having the shape of a portion of a toroid; a toroidal core of magnetic material of relatively low conductivity mounted with a portion thereof within said coils, said core having the same center of curvature as said coils and being movable therein and a layer of material of relatively high conductivity on said core covering a predetermined length of said core in a circumferential direction; means for rotating said core about its center of curvature; and switch means connected to one of said coils and adapted to short-circuit said one of said coils, said switch means being operated to its shortcircuiting position by said rotating means during movement of said high conductivity layer through the other of said coils.

15. A multi-band tuner comprising a pair of coils having the shape of a portion of a toroid mounted in spaced positions with respect to each other, said coils being connected in series with each other; a toroidal core of magnetic material of low conductivity mounted with a portion thereof within said coils, said core having the same center of curvature as said coils and being movable therein and a layer of material of high conductivity on said core covering a length of said core in a circumferential direction equal to the length of one of said coils; a rotatable shaft mounted at the center of curvature of said core and perpendicular to the plane of said core and means connecting said core to said shaft; a pair of stationary contacts, one being connected to the adjacent connected ends of said coils and the other being connected to the opposite end of the other of said coils; and means controlled with said shaft for interconnecting said stationary 10 contacts while said high conductivity layer is within said one coil.

16. A multi-band tuner comprising a, hollow coil form of insulating material having the shape of a portion of a toroid, a pair of coils having different reactance values mounted on said coil form in spaced positions with respect to each other, said coils being connected in series with each other; a toroidal core of magnetic material of low conductivity mounted with a portion thereof Within said coil form, said core having the same center of curvature as said coil form and being movable therein and a layerof material of high conductivity on said core covering substantially one-half of said core in a circumferential direction; a rotatable shaft mounted at the center of curvature of said core and perpendicular to the plane of said core and means connecting said core to said shaft; a pair of stationary contacts, one being connected to one end of the coil of higher reactance value and the other being connected to the other end of said coil of higher reactance value; and means operable by said shaft for interconnecting said stationary contacts while said high conductivity layer is within the coil of lower reactance value, said stationary contacts being electrically unconnected at other positions of said core.

17. A multi-band tuner comprising a hollow coil form of insulating material having the shape of a portion of a toroid; a pair of coils having different reactance values mounted on said coil form in spaced positions with respect to each other, said coils being connected in series with each other; a toroidal core of magnetic material of low conductivity mounted with a portion thereof within said coil form, said core having the same center of curvature as said coil form and being movable therein and a layer of material of high conductivity on said core covering substantially one-half of said core in a circumferential direction; a rotatable shaft mounted at the center of curvature of said core and perpendicular to the plane of said core and means connecting said core to said shaft; a pair of stationary contacts, one being connected to one end of the coil of higher reactance value and the other being connected to the other end of said coil of higher reactance value; and a, movable contactor mounted on said shaft, said contactor being adapted to interconnect said stationary contacts while said high conductivity layer is within the coil of lower reactance value and being out of engagement with one of said stationary contacts at other positions of said core.

18. A multi-band tuner comprising a hollow, semi-toroidal coil form comprising two substantially identical sections of insulating material each having a semi-circular cross-section; a pair of coils having different reactance values mounted on said coil form in spaced positions with respect to each other, said coils being connected in series with each other; a toroidal core of magnetic material of low conductivity mounted with a portion thereof within said coil form, said core having the same center of curvature as said coil form and being movable therein and a layer of material of high conductivity on said core covering substantially one-half of said core in a circumferential direction; a rotatable shaft mounted at the center of curvature of said core and perpendicular to the plane of said core and means connecting said core to said shaft; a pair of stationary contacts, one being connected to one end of the coil of higher reactance value and the other being connected to the other end of said coil of higher reactance value; and a movable contactor mounted on said shaft, said contactor being adapted to interconnect said stationary contacts while said high conductivity layer is within the coil of lower reactance value and being out of engagement with one of said stationary contacts at other positions of said core,

19. A multi-band tun r comprising a hollow, semi-toroidal coil form comprising two substantially identical sections of insulating material each having a semi-circular cross-section; a pair of coils having difierent reactance values mounted on said coil form in spaced positions with respect to each other, said coils being connected in series with each other; a toroidal core of magnetic material of low conductivity mounted with a portion thereof within said coil form, said core having the same center of curvature as said coil form and being movable therein and a layer of material or" high conductivity on said core covering substantially one-half of said core in a circumferential direction; a rotatable shaft mounted at the center of curvature of said core and 12 perpendicular to the plane of said core and means connecting said core to said shaft; three stationary contacts, the first of said contacts being connected to the adjacent, connected ends of said coils, a second contact being connected to the opposite end of the coil of higher reactance value and the third contact being connected to the opposite end of the coil of lower reactance value; and a movable contactor mounted on said shaft, said contactor being adapted to interconnect said first and second stationary contacts While said high conductivity layer is within the coil of lower reactance value and to interconnect said first and third stationary contacts at other positions of said core.

VINCENT P. FRIBERG.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,898,792 Shermund Feb. 21, 1933 2,280,521 Foster Apr. 21, 1942 2,394,391 Martowicz Feb. 5, 1946 2,475,032 Koch July 5, 1949 

